Assay methods utilizing immune responses have been widely used for early disease detection in the fields of clinical examinations and diagnostic pharmaceuticals. The assay methods are desired to have higher detection sensitivities. Thus, there is a great demand for increasing the sensitivities of the clinical examinations and diagnostic pharmaceuticals. In view of the sensitivity increase, assay methods utilizing fluorescence or chemiluminescence are becoming widely used instead of assay methods utilizing reactions of enzymes such as peroxidases and alkaline phosphatases. The assay methods utilizing the fluorescence or chemiluminescence are believed to be capable of detecting the presence of only one molecule of a detection subject substance theoretically. However, in practice, such a desired sensitivity has not been achieved in the methods.
In the assay method utilizing the immune response, the detection sensitivity depends on several factors. The factors include non-specific adsorption of a detection subject such as an antibody or an antigen. or a labeled substance thereof for the assay to a solid phase surface of a base body such as an immune reaction vessel or an assay instrument. In addition, in the case of using a sample containing a plurality of biomolecules such as a serum, a plasma, a cell extract, or a urine, the detection sensitivity may be deteriorated due to noise generated by non-specifc adsorption of various unspecified coexisting substances such as proteins to the solid phase surface of the base body.
In a conventional method for preventing the non-specific adsorption, a biological protein not participating in the immune response, such as a bovine serum albumin, a casein, or a gelatin, is adsorbed to the solid phase surface of the base body such as the immune reaction vessel or the assay instrument to inhibit the non-specific protein adsorption. However, the method using the biological protein such as the bovine serum albumin has problems of biotic contamination such as BSE (bovine spongiform encephalopathy) and difference between lots. Furthermore, storage temperature, duration of use, and the like of the biological protein are limited in the method.
Therefore, several protein adsorption inhibitors containing a chemically synthesized product as a main component have been proposed. Patent Publication 1 discloses a method using a polyvinyl alcohol, and Patent Publication 2 discloses a method using a polymer of 2-methacryloyloxyethyl phosphorylcholine. In these methods, the chemically synthesized product is physically adsorbed to the solid phase surface of the base body such as the immune reaction vessel or the assay instrument, to achieve a protein adsorption-inhibiting effect.
Non-Patent Publication 1 describes that a polymer compound having a phosphatidylcholine group can stabilize a protein. However, Non-Patent Publication 1 does not provide any teaching or suggestion of the protein adsorption-inhibiting effect.